9. Palindrome Problem - Tamil Explanation : LeetCode series | Problem 2
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Problem Breakdown for Beginners
A number is a palindrome if it remains the same when its digits are reversed. For example:
121 is a palindrome because it reads the same forward and backward.
121 is not a palindrome because the minus sign doesn’t appear at the end, so it reads as 121 when reversed.
Goal: We need to write a function that takes an integer x and returns true if it is a palindrome and false otherwise.
Plan to Solve the Problem
Since we’re limited to basic concepts, here’s a straightforward approach without converting the number to a string:
Check for negative numbers: If x is negative, it’s not a palindrome (e.g., -121).
Reverse the digits: Use a loop to reverse the digits of x.
Compare the reversed number to the original number:
If they are the same, x is a palindrome.
Otherwise, x is not a palindrome.
Code Explanation (Step-by-Step)
Here’s the code to implement the solution with only simple concepts like loops and conditions:
Explanation of Each Step
Check for negative numbers:
If x is negative (e.g., -121), we return false right away because negative numbers can’t be palindromes.
Reverse the number:
We initialize reversed as 0. This variable will store the reversed version of x.
We use a while loop to reverse the digits of x.
lastDigit = x % 10 gives us the last digit of x.
reversed = reversed * 10 + lastDigit appends the last digit to reversed.
x = x / 10 removes the last digit from x so we can process the next one.
Compare original and reversed numbers:
After the loop, we compare original with reversed.
If they are the same, x is a palindrome, so we return true.
If they are different, we return false.
Example Walkthrough
Example 1: x = 121
original = 121
Loop:
lastDigit = 1, reversed = 0 * 10 + 1 = 1, x = 12
lastDigit = 2, reversed = 1 * 10 + 2 = 12, x = 1
lastDigit = 1, reversed = 12 * 10 + 1 = 121, x = 0
After the loop, reversed = 121, which matches original, so the result is true.
Example 2: x = -121
Since x is negative, we return false right away.
Example 3: x = 10
original = 10
Loop:
lastDigit = 0, reversed = 0 * 10 + 0 = 0, x = 1
lastDigit = 1, reversed = 0 * 10 + 1 = 1, x = 0
After the loop, reversed = 1, which doesn’t match original, so the result is false.
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